sbuck863

My friend and I both took delivery of our C7s last week, and have different break-in philosophies. I take it a bit easy for the first 500 miles, but he breaks his cars in hard from the get-go. He says his car is backfiring on full throttle bursts. Is this anything to be concerned about, or should he take it back to the dealer for evaluation? Any feedback will be appreciated.

TEXHAWK0

No matter how you break it in, I would not be making any full throttle starts or stops. Remember, you are not just breaking in the engine, but also the transmission, differential, and brakes.

I would think that any back firing, no matter how many miles are on the car, would not be normal...

Theta

That's completely normal... It's big in the FI world, and it's a fueling/timing effect.

For example, in the MINI world it's called "pop-and-burble". I have a full race MINI and a full rally-spec MINI, and they both do it because of the timing.

The demo C7 videos all showed "backfiring" / popping on a full throttle shift. It's unspent fuel detonating in the cats (or in the case of catless, in the pipes).

Oh, and my C7 "backfires" quite often on those shifts (especially high-RPM downshifts). Completely normal. Not as fun as turbocharger fire coming out the pipes, but still nice to hear.

DDSLT5

Technically, this isn't "backfiring", but I think this is what the OP is referring to, so mission accomplished!

BRCC

Now that there have been a few out there on the street, this is relative to the A6 Z51, under full acceleration during the shifts there appears to be a bit of backfire another post above related this actually to fuel lighting up in the cats and that's what it sounds like. I am curious as to how many A6 owners have experienced this. Basically did this in the tour mode, will try it later in Sport & Track to see if results the same.

OddJob1971

I get it on my M7 when I downshift. It's especially a lot more noticeable now with the headers and off road pipe.

MoabC7

Count me in. WOT shift In Sport got my attention or maybe it was when I lifted.

SLBelt

My A6 does it and I love it!

garwood94

I thought it was the rev limiter causing the pop! I wanted my A6 to shift before it pops, but I am still learning about this C7... I do not like it as it is not a smooth acceleration if it pops between gears- duh! There is a pause in momentum when this occurs and that is not desirable IMHO.

Theta

Well, with a traditional automatic Torque Converter, you're going to have a momentary gap in acceleration., unlike DCT which already has the gear engaged.

That momentary gap may only be 500ms, but break that down at 5000rpm and you have 333 cylinder fires in that time. Of course you're going to have a burble there, as that fuel is being expended and thrown through the exhaust system un-burned.

Hell, you should hear my rally car with anti-lag.

Bill Dearborn

Actually it is 166 cylinder firings in 500ms at 5K rpm. They only fire every other revolution.

Bill

garwood94

So it appears I am stuck with this popping... Even with the cats removed, long tube headers, head work, AFM/DOD/VVT deletes, new CAI and medium size cam? I was hoping this would make it go away... I guess we'll see...

Theta

Not sure if serious....

Theta

My bad - good catch, Bill!

CPhelps

Typically headers make this much more prevalent, at least on the Gen 3/4 stuff, so if you're getting it stock, if anything I would expect it to get more so. Seems like certain exhaust combos helped to prevent it more than others though.

Mines manual, and a C5, so take it with a grain of salt, but it does it only in deceleration in gear/engine braking situations. Or holding part throttle to avoid hitting the rev limiter while keeping the revs up, staying in the gas as much as possible while upshifting, etc.

So in sport mode if the C7 is holding gears to keep you in the power band, and has the most aggressive engine programming active, staying in the throttle as much as possible to minimize the lost acceleration from cutting the power, it makes sense that the C7 could do it.